Sinuous spring structure



April 21, 1964 C. L- KRAKAUER SINUOUS SPRING STRUCTURE Filed April 3. 1962 INVENTOR.

C. Leonard Krakauer BY 4 A TZORNZY United States Patent 3,129,935 SINUOUS SPRING STRUCTURE C. Leonard Krakauer, Roslyn Heights, N.Y., assignor to Kay Manufacturing Corp., New York, N.Y., a corporation of New York Filed Apr. 3, 1962, Ser. No. 184,753 2 Claims. (Cl. 267-111) This invention relates to sinuous springs and to the seats or the like using such springs to support a cushion or upholstery.

Strips of rubber webbing stretched across a frame are frequently used to support a removable cushion or even an upholstered seat cushion. The webbing, while satisfactory for the purpose, is expensive and is being replaced by the much more economical sinuous wire springs. Such springs have cross bars connected by alternate bends or loops. The cross bars have usually been longer than the diameter of the loops. Tips are bent from the end portions of the end loops and enter pre-drilled holes in opposite rails of the frame across which the springs are arranged. The springs heretofore have ended in a semicircular loop at each end having a half cross bar extension so that the tips bent from the ends of the loops have been located at the center line of the spring.

It has been found that while such springs have been otherwise satisfactory, the wire material adjacent the fixed bent end tips are subjected to relatively high torsional, shear and multiplanar bending stresses inducing fatigue at a point near the end, and causing ultimate failure of the spring at that point.

The present invention is therefore directed to the production of a sinuous wire spring so shaped as to prevent the over-stressing of the spring beyond the limit which the spring can safely withstand under repeated applications and release of the load thereon, the over-stressing being prevented by reducing certain of the stresses at the spring end which combine to cause early fatigue failure of the spring.

The invention is further directed to the spring assembly with the frame, wherein the substantially straight off center spring tips are snugly, but not tightly, inserted into frame holes so located that the springs are properly positioned, both to give correct support and maximum free dom from stress failure.

The various objects of the invention will become clear as the description progresses and from the drawings, in which- FIG. 1 is a somewhat diagrammatic top plan View of a spring structure employing the invention.

FIG. 2 is a vertical sectional view taken on the line 22 of FIG. 1.

FIG. 3 is a fragmentary top plan view of the spring end portion assembled with a frame rail.

FIG. 4 is a vertical sectional view taken on the line 4-4 of FIG. 3.

FIG. 5 is a perspective view of a modified form of the spring wherein the spring tips are on opposite sides of the longitudinal center line of the spring.

In that form of the invention illustrated as an example, the opposite rails and 11 of the frame 12 are predrilled with transverse holes as 13 for the reception of the substantially straight tips 14 of the springs 15. Each of the springs is of sinuous or corrugated wire having a diameter slightly less than that of the holes 13 so that each tip may readily be inserted into its hole without the need for excessive force, but without being loose in the hole, the end of the spring being thereby adequately fixed to the frame.

The spring shown is preferably though not necessarily, of the flat sinuous type, meaning that except for the tips 14, the generally semi-circular alternating spring loops 16 and the cross bars 17 which the loops connect, lie in the same plane and that they tend to remain in said plane when the spring is unstressed. As shown best in FIG. 3,

laterally from the end loop 18 and is substantially perpen-,

dicular to the plane of the spring.

The location of the tip 14 is an important feature of the invention. Should such tip be arranged at the longitudinal center line of the spring in a manner not shown herein, it has been found that there then soon results a fatal defect during use which causes the spring to break by fatigue. The tip is so arranged that it is in substantial spaced relation to the center line. If it were on the center line, it would be joined to the semi-circular end loop 18 by a straight extension corresponding in length and position to about half of a cross bar 17. When a spring with such a tip end extension is loaded, the extension particularly is subjected to excessive combined complex stresses and fails by fatigue at some point in the spring end as 20. It is believed that failure by fatigue is caused by repeated combined torsional, shearing and multiplanar bending stresses. The half cross bar adjacent the tip is twisted when the body of the spring is depressed. The extension also bends downwardly and inwardly under the load, and is further subjected not only to the shearing stresses from the load, but in addition is subjected to the initial existing complex stresses in the spring due to the spring having been installed under tension.

While each individual movement of the cross bar under load and release of the spring, may be slight in itself, many repetitions thereof result in premature breakage. The useful life of the spring cannot be substantially prolonged by using an end cross bar of full or nearly full length, that is, one extending past the center line 19. The objectionable combined stresses still occur with premature failure usually resulting, at some point on the cross bar.

Nor is it practical to locate the tip at the outermost point of the last loop or bend and thereby to reduce the end loop to a half loop. Fixing the spring to the frame at such point tends to cause swaying, bulging or tipping of the spring at an angle and out of its normal proper plane. Furthermore, high combined stresses seem to ocour in the loop under these conditions since premature failure appears there.

It has been found that when substantially the entire end cross bar is eliminated, the minimal degree of combined stresses seems to occur. It is for that reason that the tip 14 has been bent from the spring end at a point near or in advance of the point 20 of the last bend 18 and in substantial transverse spaced relation to and short of the longitudinal center line 19. The fatigue life of ends having tips at this location on the spring has surprisingly been found to be very good in commercial practice and in laboratory tests.

A bend of small radius at the point 20 connects the end loop 18 with the tip 14 and may space said loop slightly above the top of the rail as 10, but since the bend wedges the loop in place against material movement, the loop does not strike the rail when the spring is loaded and therefore does not create noises when the spring is loaded and unloaded. As shown in FIG. 1, the tips 14 at both ends of the spring are on the same side of the center line 19. As shown in FIG. 5, the tips 14 and 14a are on opposite sides of the center line and help to balance the forces on the spring and to prevent possible tipping over or swaying.

It will now be seen that by the simple expedient of locating the end tip of the spring at a point which is short of or in advance of and oif the center line and at or near the end loop of the spring, certain stresses which cause Patented Apr. 21, 1964- premature failure are substantially reduced and the use ful life of the spring considerably prolonged against failure by fatigue at its end. i

I claim: 1. A flat sinuous spring having straight cross bars joined by alternating loops,

the loops and cross bars being coplanar, the end loop at each planar end portion of the spring being arcuate throughout the entire length thereof and terminating at a point in transverse spaced relation to the longitudinal center line of the spring and substantially diametrically opposite the other end of said end loop, there being a space between said point and the longitudinal center line of the spring not less in length than half the length of a straight cross bar, a substantially straight tip integral with and depending laterally from the terminal point of each end loop and thereby being arranged perpendicularly to the general plane of the loops and bars and in transverse spaced relation to the longitudinal center line of the spring and in longitudinal spaced relation to and substantially diametrically opposite said other end of said end loop, and a bend of relatively small radius integrally joining the upper end of the tip, to said end point of the end loop,

the length of the straight cross bars being less than the diameter of the loops,

the tips being on the same side of the center line and lying in a plane spaced from and parallel to the longitudinal center line of the spring,

the aforesaid space excluding excessive torsional stress upon the planar end portions of the spring when the spring is normally loaded and unloaded, and

the aforesaid bend spacing the planar end portions laterally away from the surfaces of a seat frame into which the tips are inserted.

2. In a spring seat structure,

a frame having opposed rails each having a top surface and spaced apart holes in said surface and extending downwardly therefrom,

a series of sinuous wire springs each according to claim 1 bridging the frame and each being pretensioned and having the tips thereof inserted snugly into corresponding holes of opposed rails, whereby stresses on the planar end portions of the end loops are limited to safe amounts when the structure is normally loaded and unloaded and premature breakage of said end portions by fatigue is prevented.

References Cited in the file of this patent UNITED STATES PATENTS 2,124,655 Freund July 26, 1938 2,440,001 Blumensaadt Apr. 20, 1948 3,035,828 Stubnitz May 22, 1962 

1. A FLAT SINUOUS SPRING HAVING STRAIGHT CROSS BARS JOINED BY ALTERNATING LOOPS, THE LOOPS AND CROSS BARS BEING COPLANAR, THE END LOOP AT EACH PLANAR END PORTION OF THE SPRING BEING ARCUATE THROUGHOUT THE ENTIRE LENGTH THEREOF AND TERMINATING AT A POINT IN TRANSVERSE SPACED RELATION TO THE LONGITUDINAL CENTER LINE OF THE SPRING AND SUBSTANTIALLY DIAMETRICALLY OPPOSITE THE OTHER END OF SAID END LOOP, THERE BEING A SPACE BETWEEN SAID POINT AND THE LONGITUDINAL CENTER LINE OF THE SPRING NOT LESS IN LENGTH THAN HALF THE LENGTH OF A STRAIGHT CROSS BAR, A SUBSTANTIALLY STRAIGHT TIP INTEGRAL WITH AND DEPENDING LATERALLY FROM THE TERMINAL POINT OF EACH END LOOP AND THEREBY BEING ARRANGED PERPENDICULARLY TO THE GENERAL PLANE OF THE LOOPS AND BARS AND IN TRANSVERSE SPACED RELATION TO THE LONGITUDINAL CENTER LINE OF THE SPRING AND IN LONGITUDINAL SPACED RELATION TO AND SUBSTANTIALLY DIAMETRICALLY OPPOSITE SAID OTHER END OF SAID END LOOP, AND A BEND OF RELATIVELY SMALL RADIUS INTEGRALLY JOINING THE UPPER END OF THE TIP TO SAID END POINT OF THE END LOOP, THE LENGTH OF THE STRAIGHT CROSS BARS BEING LESS THAN THE DIAMETER OF THE LOOPS, THE TIPS BEING ON THE SAME SIDE OF THE CENTER LINE AND LYING IN A PLANE SPACED FROM AND PARALLEL TO THE LONGITUDINAL CENTER LINE OF THE SPRING, THE AFORESAID SPACE EXCLUDING EXCESSIVE TORSIONAL STRESS UPON THE PLANAR END PORTIONS OF THE SPRING WHEN THE SPRING IS NORMALLY LOADED AND UNLOADED, AND THE AFORESAID BEND SPACING THE PLANAR END PORTIONS LATERALLY AWAY FROM THE SURFACES OF A SEAT FRAME INTO WHICH THE TIPS ARE INSERTED. 